The La Palma Quantum Interferometer (LPQI; https://lapalmaqi.es/) aims to open the microarcsecond angular-resolution regime in optical astronomy. It achieves this by measuring correlations between individual photons detected by widely separated optical telescopes at the Roque de los Muchachos Observatory (ORM). The initial deployment, LPQI-Pathfinder, will operate between the NOT and TNG,...
Traditional stellar astrophysics has long relied on the assumption of spherical symmetry, an approximation that breaks down for several stellar objects, e.g. rapid rotators and close binaries. In particular, for rapidly rotating stars, strong centrifugal forces induce substantial geometric deformation, producing an oblate stellar shape together with **non-uniform surface gravities and...
We present an enhanced near‑infrared heterodyne interferometry testbed developed at the Max Planck Institute for Physics (MPP)
to complement ongoing advances in both direct‑detection and stellar intensity interferometry techniques. The upgraded setup incorporates
a new, narrow‑linewidth 1550 nm local-oscillator laser, with improved optical stability, and a programmable optical delay line...
Generative models have found widespread applicability for inverse problems, including image reconstruction for interferometers. I will describe examples of Bayesian image reconstruction for intensity interferometry using modern diffusion models. This enables multiple new science applications, including probes of the interiors of dwarf stars, the atmospheres of exoplanets, and the horizons of...
The ASTRI Stellar Intensity Interferometry Instrument (SI3) is currently being integrated on the ASTRI Mini-Array at the Teide Observatory (Tenerife, Spain). In parallel with the instrument deployment, we are developing the data analysis framework and simulation tools required to exploit the unique capabilities of SI3 and to support the commissioning phase. We present the analysis pipeline...
I will discuss the status of the discussions with ESO and the "VLT2030" and "Expanding Horizons" proposal calls.
This work investigates the feasibility of carrying out stellar photon-correlation measurements using the 1.3 m Devasthal Fast Optical Telescope (DFOT) at the ARIES Devasthal Observatory near Nainital, India. The experiment will use Becker & Hickl hybrid photodetectors in a two-detector Hanbury Brown–Twiss configuration. This detector system was previously used for photon-correlation...
Precise measurement of the Hubble constant depends on anchoring the cosmic distance ladder with direct stellar measurements. I propose a precision intensity interferometry program to measure red-clump star angular sizes, providing a new observational foundation for distance-ladder calibration. I also present pathways to detect spacetime foam—a quantum-gravity prediction—through high-precision...
Precision timing is of the essence in intensity interferometry. Whether the task involves the temporal tagging of single photons or the continuous acquisition of photocurrents over time, measuring the Hanbury-Brown and Twiss effect between distant telescopes necessitates the stable sampling of signals at well-determined times throughout the night of observation. The advent of photodetectors...
Following the design phase and laboratory testing of the prototype, the development of the ASTRI Stellar Intensity Interferometry Instrument (SI3) entered the crucial hardware integration phase at the end of 2025. The process of integrating this system into the array involves rigorous testing of all electronic and optical components, with particular attention to the critical challenge of...
The sensitivity achievable with stellar intensity interferometers using Imaging Atmospheric Cherenkov Telescopes (IACTs) can be significantly enhanced with the use of ultra-fast single-photon detectors. Conventional inter-telescope baselines of ∼100 m probe angular scales of order ~1 mas, while correlations between sections of a telescope mirror provide access to larger structures of order >~...
THE PAST: Concepts of astronomical interferometry were proposed by Fizeau in the 1860’s and tried out by Stéphan in Marseille some decade later. After achieving the first successful stellar observations on Mt.Wilson around 1920, the field saw little development until Hanbury Brown and Twiss measured intensity correlations in the 1950’s. The Narrabri intensity interferometer followed, but its...
Massive binary systems provide fundamental constraints on stellar evolution through indirect measurements of stellar masses, radii, and distances. However, systems characterized by milli-arcsecond angular separations require interferometric techniques to resolve these parameters. Stellar Intensity Interferometry (SII), pioneered by the Narrabri Stellar Intensity Interferometer in the 1970s,...
Modern single-photon detector arrays make it possible to rethink the readout concept for stellar intensity interferometry (SII). While ultrafast single-photon detectors targeting a single spectral line are already being explored by several groups, a key step forward is the use of detector arrays with multiple independently read out channels, enabling simultaneous photon detection of a large...
Like intensity interferometry, optical heterodyne interferometry offers a compelling and scalable alternative to direct interferometry for hectometric/kilometric baselines. However, it is well known that direct detection of light outcompetes coherent heterodyne detection in terms of signal-to-noise ratio at optical wavelengths, not only because of the narrow (<100 GHz) electronic bandwidth of...
I will discuss the progress we have made since the workshop of Weischenfeld, more specifically on the optical system and on the
QUASAR1 spad array chip.
We'll report on the development of a high time-resolution optical intensity-interferometry system based on SPAD arrays. Two existing 512×1 SPAD Linospad2 detector chips were used to validate the instrument architecture, including spectrometer, wavelength multiplexing, correlator performance and clock synchronization. A set of 4 FPGA boards achieves a synchronization precision of approximately...
Stellar Intensity Interferometry (SII) is undergoing a major revival [1,2], yet its sensitivity remains bound by the performance of traditional photon counters. For SII in 500-700 nm range, standard avalanche photodiodes (APDs) enjoy a relatively high quantum efficiency but suffer from timing jitter, which directly affects the measurable second-order correlation.
In this work, we present the...
The existence of natural lasing lines in the environment of Eta Carinae is predicted by a multitude of spectral observations. Could these lines be produced by "random lasers", where traditional cavities don't exist but light feedback is supplied by scattering of the photons within the medium itself? Different emission lines in the spectrum of Eta Carinae between 960 nm and 1.7 micrometers are...
The VERITAS Collaboration has performed stellar intensity interferometry analysis on the binary system Spica, based on data accumulated over a period of five years. Extended observations with six indepdendent baselines provided good coverage of the Fourier (u,v) plane with high signal-to-noise. The intensity pattern was measured over several cycles of the 4.01-day orbit and is well...
Intensity Interferometry (II) has demonstrated significant potential for high-angular-resolution measurements of stellar objects, as the recent one with VERITAS, which resolved non-spherical structure. However, these studies assume simplified stellar models with static surface brightness, which limits our ability to investigate the effects of realistic stellar structure and shape.
There is an...
Intensity interferometry in the optical band has experienced a notable resurgence, largely driven by the adaptation of Cherenkov telescope arrays designed for gamma-ray astronomy. This contribution explores the scientific potential of the thousands of baselines and kilometre-scale extent of the Cherenkov Telescope Array Observatory (CTAO) as an optical interferometer, as well as the technical...
Recent advances in single-photon detection technology have opened entirely new opportunities for stellar intensity interferometry (SII). In this talk, we present the concept and current development status of SII measurements with the new MAST array. The array consists of twenty 60 cm telescopes, providing a total effective collecting area comparable to that of a single 2.7 m telescope, while...
The ASTRI Mini-Array is an International collaboration, led by INAF, that is constructing and operating an array of nine Cherenkov Telescopes at the Teide Observatory (Tenerife, Spain). The ASTRI Stellar Intensity Interferometry Instrument (SI3) is a fast single-photon-counting instrument for performing intensity interferometric observations of bright stars with the ASTRI Mini-Array. It will...
The VERITAS Stellar Intensity Interferometer (VSII) has been performing observations of bright (OBA) stars in the visible waveband (416 nm) since 2019. Over 1000 hours of bright- and dark-sky VSII observations have been made on 58 bright stars, fast rotators, and multi-star systems, forming the VSII Northern Hemisphere Survey. In this talk, we will present the first results from the analysis...
Roughly one in a thousand quasars or bright galaxies at cosmological distances appears to us as a multiple-image mirage, caused by gravitational lensing by an intervening galaxy or cluster. The separation between the multiple images ranges from sub-arcsecond to tens of arcseconds, which is easily resolved by standard telescopes. These are sometimes called macro-images.
Each macro-image...
IC4Stars (Intensity Correlations For Stars) is a project that aims to directly measure the angular diameter of the white dwarf Sirius B. Together with the high-precision distance measurement from Hipparcos parallaxes, this will provide a measurement of the physical size of a white dwarf star for the first time. The objective is to perform intensity interferometry measurements deployed at two...
The poster will show our assembled spectrometer - spad array, alignment issues and details, spad array delay characterization, and very preliminary bench results. Unsolved issues will be listed as topics for discussion to encourage discussion and brainstorm solution space.
